Remote pressure measuring apparatus and method



June 28, 1966 1.. ALTMAN ETAL 3,257,351

REMOTE PRESSURE MEASURING APPARATUS AND METHOD Filed Feb. 10, 1964 FIG. I

FIG. 2

: INVENTORS.

LAWRENCE ALTMAN DONALD GERTZ WILLIAM F. SEIBOLD United States Patent REMOTE PRESSURE MEASURING APPARATUS AND METHOD Lawrence Altman, New York, and Donald Gertz, Carle Place, N.Y., and William F. Seibold, Arnold, Md., assignors, by direct and mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Filed Feb. 10, 1964, Ser. No. 343,907 4 Claims. (Cl. 73-406) The present invention relates to the remote instrumentation of a vessel and more particularly, to the remote instrumentation of a vessel utilizing acoustical sensing techniques for the measurement of fluid pressure.

The development of the nuclear reactorhas created a great deal of interest in device-s which are capable of instrumenting the interior of a closed vessel with respect to such conditions as liquid level, temperature, and pressure, as well as others. The presence within the vessel of radioactive materials makes it most desirable to eliminate or at least minimize the possibility of leakage from the vessel at locations where instrumentation leads pass through the vessel wall. Even though sophisticated seals are developed and utilized, in time there is apt to be a deterioration of materials and there is increased possibility that some leakage will occur.

In addition, it is well known that instrumentation of a nuclear reactor represents a substantial portion of the capital costs and is a major item in maintenance, spare parts, calibration, training, and downtime resulting from instrumentation failure.

In a pressurized water reactor, instrumentation includes sensing devices within the reactor vessel to monitor such conditions as pressure, temperature, and liquid level. It is necessary, of course, in conventional arrangements to transfer the developed signals by way of leads through openings provided in the vessel wall. Aside from the possibility of leaks which can develop in such a construction, the failure of some of the sensing devices within the vessel presents diflicult problems of maintenance. In addition, the sensing signals produced are usually analog in nature so that background noise, power supply variations, calibration uncertainties and instrument drift quite often interfere with the accuracy of the readings. Also, an analog signal is not compatible with modern digital control systems so that additional expensive equipment is required to convert the information into digital form.

Thus it has long been felt in the nuclear power reactor art and in other areas where the need has appeared that simplified and more reliable measuring devices are required, especially those which can produce the desired information directly in digital form and can avoid contamination from the contents of the nuclear reactor or other containment vessels. The best types of measuring devices would be those which are externally mounted but are capable of sensing the various conditions Within the reactor vessel and can produce the information in digital form.v Devices of this nature would be relatively unaffected by environmental changes and power supply variations, not subject to drift, and would be easy to maintain since the units are replaceable without opening the reactor vessel.

While the example of the nuclear reactor emphasizes the need for such types of instrumentation, it is also true that equipment of this type would be useful wherever and whenever the convenience and safety of this type of instrumentation is desirable such as in general process plants, petroleum plants, fuel tanks, etc.

circuits 77 complete the arrangement.

3,257,851 Patented June 28, 1966 Efforts have been made to adapt acoustical techniques to the satisfaction of this need, as evidenced by US.

' Patent No. 3,100,885 dated August 13, 1963, which relies on liquid-air or liquid-gas interface to reflect the sound waves introduced'in the liquid from outside the vessel. However, while arrangements of this type represent substantial improvements in the art, they do not solve the problem of pressure determination, and, also, further improvements are possible in accordance with this invention to improve the nature of the signal output so as to be digital in form. This output is then suitable for direct utilization in modern digital information computers and eliminates a possible ambiguity which could occur with reliance solely on the liquid-air or liquid-gas interface as a contact surface.

The present invention meets the requirements set'forth above for improved instrumentation of nuclear reactors and other devices by offering apparatus and method capable of sensing the pressure of a fluid within a vessel by an external arrangement of liquid level measurement pressure within the vessel is transmitted by way of a diaphragm arrangement to a stillwell in which a liquid is maintained at a level representing the fluid pressure. An acoustical transducer is mounted externally of the stillwell to inject sound pulses into the liquid medium. These are reflected by a stepped device within the liquid to indicate the level of liquid within. This information is produced directly in digital form due to the stepped reflector and is usable directly in digital systems,

It is thus a first object of this invention to provide an arrangement for measuring fluid pressure Within a closed vessel.

A further object of this invention is the application of remote sensing of liquid level to the measurement of fluid pressure within a vessel and the direct production of this information in digital form.

Still another object of this invention is the remote measurement of pressure of a fluid within a vessel through the use of acoustical transmitting and receiving devices.

Other objects and advantages of this invention will hereinafter become obvious from the following description of a preferred embodiment of this invention taken with the accompanying drawings in which:

FIG. 1 is an elevational view in section of a vessel provided with a preferred embodiment of this invention for the measurement of fluid pressure; and

FIG. 2 is an isometric view of the step shaft reflector.

Referring to FIG. 1 there will be seen a vessel 12 containing liquid 14. An acoustical standpipe 62 is located adjacent to vessel 12 andthey are interconnected by way of a diaphragm chamber 64. A diaphragm 66 of suitable material separates liquid 14 from liquid 68 within standpipe 62. Liquid 68 may be Water. Diaphragm 66 is pressure sensitive so that the movement of the latter due to changes in vessel pressure will be communicated to standpipe 62 where the liquid level therein will be altered accordingly. A stepshaft reflector 18 within standpipe 62, a transducer 74 externally mounted in holder 75 as illustrated, and circuitry 76 to driver and receiving As the level of liquid 68 will indicate the pressure within vessel 12, transducer 74 will function with stepshaft reflector 118 to produce a digital signal indicative of the pressure within vessel 12. An inert, low absorption gas such as argon fills the space of the liquid level in standpipe 62. Trans-. ducer 74 is a piece of material exhibiting the. well known piezoelectric effect, that is, it is capable of converting an electrical pulse to a pulse of ultrasonic energy, and vice versa. An example of such a material is lead zirconate titanate. The driving and receiving circuits 77 are conventional circuits designed to initiate and receive electrical pulses. Typical circuits are described in the report NYO 10601 (FIGS. 6.2.13 and 6.3.3) issued by the US. Atomic Energy Commission. Such circuits are also commercially available.

In the operation of the level indicating apparatus, transducer 74 issues a sound pulse in response to an electrical pulse which travels through water 14 until reaching stepshaft 18. Each of the separate steps 19 below the upper surface of water 14 produces a reflected sound pulse. Due to the uniform area of the steps, the reflected pulses are of substantially the same amplitude and return to transducer 74 at predetermined time intervals. In certain instances it may be desirable to have steps of nonuniform clepth thereby transmitting pulses in non-uniform time intervals. The number of pulses returning will be a direct indication of where the liquid appears on stepshaft 18 as the sound waves do not pass through the surface of liquid '14 and only the immersed steps 19 produce reflected pulses.

While stepshaft 18 has been shown in FIG. 1 only schematically, reference is made to FIG. 2 for details of the design. There it will be seen that stepshaft 18 may be machined from a cylindrical member 34 from which a plurality of spirally-arranged wedge shaped steps 36 are cut, so that stepshaft 18 occupies a minimum of space.

Bonding of the transducer crystal to the outer surface of the vessel in the arrangement described above can be accomplished either by the use of metal bearing electricity conductive epoxies or alloy solders. In using an epoxy, the crystal is clamped to the wall by suitable means with a layer of epoxy in between and heat supplied to cure the epoxy. Care must be exercised to remove all air bubbles, and this may be facilitated by curing the epoxy in a vacuum to help eliminate the air bubbles. A suitable solder is the lead-tin eutectic with 2% silver. The alloy solder technique was successfully tested at 435 F. and was applied using the same procedure followed in the case of the epoxy.

For conditions in which the above bonding techniques might not be convenient, as under emergency replacement of a transducer, a so-called dry bonding technique has proved to be satisfactory. This technique employs optical flat mating surfaces and use of pressure to obtain the required intimacy of contact.

With regard to the acoustically reflective stepshaft, described above, the surfaces of the steps which are parallel to the transducer are arcs of circles. Experimental evidence indicates that equal areas reflect approximately equal amounts of ultrasonic energy even though each step is at a different distance from the transducer. This was noted to be true over lengths of 3 feet or less for Water since attenuation in the latter is small.

Experiments were conducted on the stepshaft to determine its limiting or critical conditions. It was found that the nature of the step surface, i.e., rough or smooth, did not affect significantly the sharpness or size of the reflected pulses. However, surfaces inclined only slightly, i.e. 7, away from the transducer reflected only a small amount of energy to the transducer so that the surfaces should be substantially parallel to or facing the transducer. Corrosion of the surface likewise did not affect the shaft performance.

In addition, a crystal frequency of about 4 .mc. was found to be best for applications of medium range and resolution in water. Higher frequencies attenuate too rapidly while lower frequencies produce less sharply defind reflections. A crystal diameter slightly greater than stepshaft diameter provided superior results. For example, a stepshaft diameter of 1.85 inches was used with a 2 inch diameter crystal with excellent results.

Experiments with both a solid state driver and a vacuum tube ultrasonic generator showed that input power and voltage were not critical factors. Reduction of driver voltage by 50% resulted in approximately a 10% reduc-- tion in reflected signal, with no effect on signal sharpness, so that the amount of power used is not a critical factor except that sufficient power should be used to obtain the desired amplitude of reflected pulses.

It has already been noted that a signal magnitude is directly related to the reflecting step area. Doubling the segment angle of a step, approximately doubles the magnitude of the signal. Regarding the mechanical alignment of the stepshaft, this is important but not critical. Alignment was found to be relatively easy for short stepshafts i.e. 18 inches in length or less, and more diflicult for long stepshafts of the order of 3 feet or more, as would be expected. Good results have been obtained using a 3 foot long, 1.85 inch diameter stepshaft with 9 equally spaced steps, pulsed by a 2 inch diameter 4 me. crystal bonded on a 0.265" stainless steel wall.

It is thus seen that there has been provided a unique approach to the remote sensing of fluid pressure within a closed container and the direct production of the information in digital form. While a preferred embodiment of this invention has been described it is understood that the scope of the invention is to be limited only by the appended claims.

We claim:

1. Apparatus for the measurement of the pressure of a fluid within a main vessel comprising an auxiliary vessel partially filled with a liquid, means for transmitting said pressure into said auxiliary vessel to support said liquid at a level to balance said pressure, means for issuing an acoustic pulse through the wall of said auxiliary vessel into said liquid, and other means within said auxiliary vessel for receiving said pulse and returning a series of spaced pulses the number of which are a function of said liquid level and thereby indicating the pressure of said fluid, said issuing means being capable of receiving said returning pulses.

2. The apparatus of claim 1 in which said transmitting means consists of an enclosed chamber, a diaphragm dividing said chamber into first and second portions and means communicating the first portion with the interior of said main vessel and the second portion with the liquid in said auxiliary vessel.

3. Pressure measuring apparatus for connection to a main vessel containing a fluid under pressure comprising an auxiliary vessel, conduit means open to and between said .main and auxiliary vessels, means including a flexible diaphragm in said conduit means for sealing said conduit against flow through said conduit means, a liquid partially filling said auxiliary vessel and said conduit means up to said diaphragm, variations in pressure in said main vessel causing said diaphragm to flex and adjust the level of liquid in said auxiliary vessel to balance the pressure in said main vessel, transmitting and receiving transducer means attached to the bottom of said auxiliary vessel for emitting a sound pulse through the vessel wall into said liquid, stationary means partially immersed in said liquid within said vessel, the latter said means having a series of vertically staggered reflective surfaces facing said transducer means for reflecting from the surfaces located beneath the surface of said liquid the sound pulse arriving from said transducer means, the number of the reflected sound pulses thereby indicating the level of said liquid within said vessel and pressure of said fluid in said main vessel.

4. The method of measuring the pressure of a fluid within a closed container comprising the steps of providing an auxiliary vessel containing a liquid, communicating by conduit the interior of said container with said vessel, inserting a diaphragm in said conduit between said vessel and container to prevent flow therebetween,

3,257,s51 5 a 6 said diaphragm flexing under changes in fluid pressure References Cited by the Examiner and changing the level of liquid in said vessel, injecting UNITED STATES PATENTS an ultrasonic pulse generally up into said liquid toward the upper level thereof in said vessel, reflecting said pulse 5 9 Theobald 73-299 at spaced intervals within said liquid, and receiving the 5 3,214,974 11/ 1965 an t a1. 73-290 reflected pulses the number of which indicating the level of said liquid and the pressure of said fluid. LOUIS PRINCE, Primary Examiner- 

3. PRESSURE MEASURING APPARATUS FOR CONNECTION TO A MAIN VESSEL CONTAINING A FLUID UNDER PRESSURE COMPRISING AN AUXILIARY VESSEL, CONDUIT MEANS OPEN TO AND BETWEN SAID MAIN AND AUXILIARY VESSELS, MEANS INCLUDING A FLEXIBLE DIAPHRAGM IN SAID CONDUIT MEANS FOR SEALING SAID CONDUIT AGAINST FLOW THROUGH SAID CONDUIT MEANS, A LIQUID PARTIALLY FILLING SAID AUXILIARY VESSEL AND SAID CONDUIT MEANS UP TO SAID DIAPHRAGM, VARIATIONS IN PRESSURE IN SAID MAIN VESSEL CAUSING AID DIAPHRAGM TO FLEX AND ADJUST THE LEVEL OF LIQUID IN SAID AUXILIARY VESSEL TO BALANCE THE PRESSURE IN SAID MAIN VESSEL, TRANSMITTING AND RECEIVING TRANSDUCER MEANS ATTACHED TO THE BOTTOM OF SAID AUXILIARY VESSEL FOR EMITTING A SOUND PULSE THROUGH THE VESSEL WALL INTO SAID LIQUID, STATIONARY MEANS PARTIALLY IMMERSED IN SAID LIQUID WITHIN SAID VESSEL, THE LATTER SAID MEANS HAVING A SERIES OF VERTICALLY STAGGERED REFLECTIVE SURFACE FACING SAID TRANSDUCER MEANS FOR REFLECTING FROM THE SURFACES LOCATED BENEATH THE SURFACE OF SAID LIQUID THE SOUND PULSE ARRIVING FROM SAID TRANSDUCER MEANS, THE NUMBER OF THE REFLECTED SOUND PULSES THEREBY INDICATING THE LEVEL OF SAID LIQUID WITHIN SAID VESSEL AND PRESSURE OF SAID FLUID IN SAID MAIN VESSEL. 